Myocardial Infarction Dr Isazadehfar Background Myocardial Infarction is

Myocardial Infarction Dr Isazadehfar

Background Myocardial Infarction is the rapid development of myocardial necrosis by a critical imbalance between oxygen supply and demand to the myocardium

Classification Acute coronary syndromes include ST-elevation MI (STEMI) Non ST-elevation MI ( NSTEMI) Unstable Angina Cardiac markers in circulation indicates myocardial infarction and help categorize MI and is a useful adjunct to diagnosis

Classification Anatomic or morphologic Transmural= Full thickness Non- transmural= Partial thickness ECG Q wave MI Non Q wave MI Does not distinguish transmural from a nontransmural MI as determined by pathology

Prevalence Increase in the proportion of NSTEMI compared to STEMI

History The history is critical in making the diagnosis of MI and sometimes provide only the only clues that lead to the diagnosis in the initial phase of presentation

History Chest Pain- anterior precordium tightness Pain may radiate to jaw, neck and epigastrium Dyspnea - angina equivalent, poor LV function Nausea/abdominal pain with posterior MI Anxiety

History Nausea with and without vomiting Diaphoresis or sweating Syncope or near syncope Elderly present with MS changes, fatigue, syncope or weakness As many as half of MI are clinically silent

Physical exam The physical exam can often be unremarkable Hypertension Hypotension Acute valvular dysfunction may be present Rales Neck vein distention

Physical Third heart sound may be present A fourth heart sound poor LV compliance Dysrhythmias Low grade fever

Causes Most frequent cause is rupture of an atherosclerotic lesion within coronary wall with subsequent spasm and thrombus formation Coronary artery vasospasm Ventricular hypertrophy Hypoxia Coronary artery emboli

Causes Cocaine Coronary anomalies Aortic dissection Pediatrics Kawasaki disease, Takayasu arteritis Increased afterload which increases myocardial demand

Risk factors for atherosclerosis Age Male gender Smoking Hypercholesterolemia and triglyceridemia Diabetes Mellitus Poorly controlled hypertension Type A personality

Risk factors for atherosclerosis Family History Sedentary lifestyle

Differentials Acute coronary syndrome Anxiety Aortic stenosis Asthma Cholecystitis and biliary colic Cholethiasis COPD

Differentials Aortic Dissection Endocarditis Esophagitis Shock Myocarditis Pericarditis Pulmonary embolism

Mechanisms of Myocardial damage The severity of an MI is dependent of three factors The level of the occlusion in the coronary The length of time of the occlusion The presence or absence of collateral circulation

Cardiac Biomarkers Cardiac biomarkers are protein molecules released into the blood stream from damaged heart muscle Since ECG can be inconclusive , biomarkers are frequently used to evaluate for myocardial injury These biomarkers have a characteristic rise and fall pattern

Troponin T and I These isoforms are very specific for cardiac injury Preferred markers for detecting myocardial cell injury Rise 2 -6 hours after injury Peak in 12 -16 hours Stay elevated for 5 -14 days

Creatinine Kinase ( CK-MB) Creatinine Kinase is found in heart muscle (MB), skeletal muscle (MM), and brain (BB) Increased in over 90% of myocardial infraction However, it can be increased in muscle trauma, physical exertion, post-op, convulsions, and other conditions

Creatine Kinase (MB) Time sequence after myocardial infarction Begins to rise 4 -6 hours Peaks 24 hours returns to normal in 2 days MB 2 released from heart muscle and converted to MB 1. A level of MB 2 > or = 1 and a ratio of MB 2/MB 1 > 1. 5 indicates myocardial injury

Myoglobin Damage to skeletal or cardiac muscle release myoglobin into circulation Time sequence after infarction Rises fast 2 hours Peaks at 6 -8 hours Returns to normal in 20 -36 hours Have false positives with skeletal muscle injury and renal failure

Renal Failure and Renal Transplantation Diagnostic accuracy of serum markers of cardiac injury are altered in patients with renal failure Cardiac troponins decreased diagnostic sensitivity and specificity in patients receiving renal replacement therapy Current data show levels of troponin I are unaltered while levels of troponin T may be elevated

CBC is indicated if anemia is suspected as precipitant Leukocytosis may be observed within several hours after myocardial injury and returns to levels within the reference range within one week

Chemistry Profile Potassium and magnesium levels should be monitored and corrected Creatinine levels must be considered before using contrast dye for coronary angiography and percutanous revascularization

C-reactive Protein (CRP) C- reactive protein is a marker of acute inflammation Patients without evidence of myocardial necrosis but with elevated CRP are at increased risk of an event

Chest X-Ray Chest radiography may provide clues to an alternative diagnosis ( aortic dissection or pneumothorax) Chest radiography also reveals complications of myocardial infarction such as heart failure

Echocardiography Use 2 -dimentional and M mode echocardiography when evaluating overall ventricular function and wall motion abnormalities Echocardiography can also identify complications of MI ( e. g. Valvular or pericardial effusion, VSD)

Electrocardiogram A normal ECG does not exclude ACS High probability include ST segment elevation in two contiguous leads or presence of q waves Intermediate probability ST depression T wave inversions are less specific

Localization of MI ST elevation only Inferior wall- II, III, a. VF Lateral wall_ I, a. VL, V 4 -V 6 Anteroseptal- V 1 -V 3 Anterolateral- V 1 -V 6 Right ventricular- RV 4, RV 5 Posterior- R/S ratio >1 in V 1 and T wave inversion

Therapy The goals of therapy in AMI are the expedient restoration of normal coronary flow and the maximum salvage of functional myocardium

Antiplatelet Agents Aspirin at least 160 mg immediately Interferes with function of cyclooxygenase and inhibits the formation of thromboxane ASA alone has one of the greatest impact on the reduction of MI mortality. Clopidogrel, ticlopidine, have not been shown in any large scale trail to be superior to Aspirin in acute MI

Supplemental Oxygen Because MI impairs the circulatory function of the heart, oxygen extraction by the heart and other tissues may be diminished Supplemental oxygen should be administered to patient with symptoms and or signs of pulmonary edema or pulse oximetry readings less than 90%.

Nitrates IV nitrates to all patients with MI and congestive heart failure, persistent ischemia, hypertension, or large anterior wall MI Primary benefit vasodilator effect Metabolized to nitric oxide in the vascular endothelium, relaxes endothelium Vasodilatation reduces myocardial oxygen demand preload and afterload

Beta-blockers Recommended within 12 hours of MI symptoms and continued indefinitely Reduces Myocardial mortality by decreasing arrythmogenic death Decrease the rate and force of myocardial contraction and decreases overall oxygen demand

Unfractionated heparin Forms a chemical complex with antithrombin III inactivates both free thrombin and factor Xa Recommended in patients with MI who undergo PTCA or fibrinolytic therapy with alteplase

Low-molecular weight heparin Direct activity against factors Xa and IIa Proven to be effective in treating ACS that are characterized by unstable angina or non ST- elevation MI Their fixed doses are easy to administer and laboratory testing to measure their therapeutic effect is not necessary makes them attractive alternative of unfractionated heparin

Thrombolytics Indicated with MI and ST segment elevation greater than 0. 1 m. V in 2 contiguous ECG leads, or new onset LBBB, who present less than 12 hours but not more than 24 hours after symptom onset The most critical variable in achieving successful fibrinolysis is time form symptom onset to drug administration

Thrombolytics As a class the plasminogen activators have been shown to restore coronary blood flow in 50 -80% of patients Contraindication active intracranial bleeding, CVA 2 months, CNS neoplasm, HTN, coagulopathy Retaplase slightly higher angiographic patency but did not translate into survival benefit Intracranial bleed risk major drawback

Percutanous Coronary Intervention Alternative if performed by skilled operator in an experienced center Standard is a “ door to balloon” time of 90 minutes PCI can successfully restore coronary blood flow in 90 to 95% of MI patients PCI definitive survival advantage over fibrinolytics for MI patients who are in cardiogenic shock

Surgical Revascularization Emergent or surgical revascularization in setting of failed PTCA in patients with hemodynamic instability and coronary anatomy amendable to surgical grafting Also indicated of mechanical complications of MI including VSD, free wall rupture, or acute MR Carries a higher risk of perioperative mortality than elective CABG

Lipid Management All post MI patients should be on AMA step II diet ( < 7% of calories from saturated fats) Post MI patients with LDL > 100 mg/dl are recommended to be on drug therapy to try to lower levels to <100 mg/dl Recent data indicate that all MI patients should be on statin therapy, regardless of lipid levels or diet

Long term Medications Most oral medications instituted in the hospital at the time of MI are continued long term Aspirin, beta blockers and statin are continued indefinitely ACEI indefinitely in patients with CHF, ejection fraction <. 40, hypertension, or diabetes

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